Seismic breakthrough reveals world below our feet
Earthquakes and volcanic eruptions are violent reminders that events on the surface are connected to processes deep within the Earth. “The reason these phenomena exist is because the mantle, which extends halfway down to the centre of the Earth, is moving,” explains ATUNE project coordinator Arwen Deuss from the University of Utrecht in the Netherlands. “If we want to know why some places have really big volcanic eruptions, then we need to know what is happening below us.”
Measuring seismic waves
To build a picture of what is occurring, scientists like Deuss detect and measure the seismic waves produced by earthquakes. “These waves can travel from, say, New Zealand all the way to Europe,” she says. “Seismometers in Europe then record these waves in a seismogram.” Deuss compares her job to giving the planet a sort of ‘brain scan’. The end result of scanning seismic waves is an image of how fast the waves travel inside the Earth. These velocities are typically coloured red for slow, and blue for fast. “We first determine whether waves are fast or slow,” adds Deuss. “Then we assume that waves go slow when they go through hot material, but it might not just be temperature that influences wave speed.”
Focus on energy
The ATUNE project, which was supported by the European Research Council, sought to expand our seismic knowledge by developing a way of measuring not just whether waves are fast or slow, but also the extent to which they lose energy, a process called damping. “The analogy I like to use for this is going for a run,” says Deuss. “If it’s hot outside, you can’t run very fast, and you’ll slow down and you also lose a lot of energy. The same happens with seismic waves. But your slow pace and low energy could also be due to another energy-sapping factor, like running on loose sand – it might not necessarily be temperature.” Deuss applied complicated mathematics to determine where in the mantle seismic waves were losing energy, and made use of a bank of supercomputers to carry out mathematical calculations. This enabled her to develop a model which shows for different regions in the mantle how quickly the energy from a major earthquake event dissipates. This model should in future help seismologists gain a fuller picture of the Earth’s complex dynamics.
The project team also made an additional, unexpected discovery. In two massive continent-sized regions of the mantel below Africa and the Pacific, Deuss was able to show that energy dissipates very slowly. This observation can be explained by the larger size of mineral crystals found here, which plays a major stabilising role. This helps to explain for example why volcanoes found above these regions, such as Hawaii, have been in place for hundreds of millions of years. “These regions appear to act as mantle anchors,” she remarks. “This could change our view of plate tectonics.” Indeed, this discovery has opened up new avenues of research for Deuss. She is currently working on a project proposal together with a geologist, a volcanologist and a geochronologist, with the aim of better understanding how our mantle changes over time. “As a seismologist I can only really provide a snapshot of today,” she explains. “But if we add history and time, and include what is happening at the surface, then we can better understand the evolution of our planet.”
ATUNE, volcanic, earthquakes, mantle, seismic, seismologist, energy